AperTO - Archivio Istituzionale Open Access dell'Università di Torino Impact of the Asian wasp Dryocosmus kuriphilus (Yasumatsu) on cultivated chestnut: Yield loss and cultivar susceptibility This is the author's manuscript Original Citation: Availability: This version is available http://hdl.handle.net/2318/1528910 since 2015-11-20T17:23:11Z Published version: DOI:10.1016/j.scienta.2015.10.004 Terms of use: Open Access Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. (Article begins on next page) 02 October 2021 This Accepted Author Manuscript (AAM) is copyrighted and published by Elsevier. It is posted here by agreement between Elsevier and the University of Turin. Changes resulting from the publishing process - such as editing, corrections, structural formatting, and other quality control mechanisms - may not be reflected in this version of the text. The definitive version of the text was subsequently published in [http://dx.doi.org/10.1016/j.scienta.2015.10.004 ]. You may download, copy and otherwise use the AAM for non-commercial purposes provided that your license is limited by the following restrictions: (1) You may use this AAM for non-commercial purposes only under the terms of the CC-BY-NC-ND license. (2) The integrity of the work and identification of the author, copyright owner, and publisher must be preserved in any copy. (3) You must attribute this AAM in the following format: Creative Commons BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/deed.en), [+http://dx.doi.org/10.1016/j.scienta.2015.10.004 ] IMPACT OF THE ASIAN WASP DRYOCOSMUS KURIPHILUS (YASUMATSU) ON CULTIVATED CHESTNUT: YIELD LOSS AND CULTIVAR SUSCEPTIBILITY Sartor C. 1) , Dini F. 2), Torello Marinoni D. 1) , Mellano M.G. 1) , Beccaro G.L. 1) , Alma A. 1) , Quacchia A. 3) , Botta R. 1) 1) Dipartimento di Scienze Agrarie, Forestali, Alimentari – DISAFA, Università degli Studi di Torino, L.go P. Braccini 2, 10095 Grugliasco (Torino), Italy. 2) Former grant holder at Dipartimento di Colture Arboree, Università degli Studi di Torino, L.go P. Braccini 2, Grugliasco (TO) 3) Former grant holder at DIVAPRA, Università degli Studi di Torino, L.go P. Braccini 2, Grugliasco (TO) ([email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] ) Corresponding author: Roberto Botta postal address: L.go P. Braccini 2, 10095 Grugliasco (TO), Italy. e-mail address: [email protected] telephone: +39 011 6708800 fax: +39 011 6708658 ABSTRACT Dryocosmus kuriphilus is the most impactful alien pest of chestnut currently reported in almost the whole Europe after its accidental introduction in Piemonte (North-west Italy) where it was found for the first time in 2002. The Piemonte Region Administration funded a project aimed to find control solutions based on both the biological control of gall-wasp and the study of plant response. This work was carried out from 2004 to 2013 and reports studies on assessment of production loss (2006-2012), cultivar susceptibility (2004-2013) and amount of nutrients subtraction caused by the insect (2012). The assessment of yield loss showed that infestation values (G/B=No. galls/bud) lower than 0.3 G/B caused no significant losses; values between 0.3-0.6 G/B originated a moderate decrease in productivity. A drastic decrease of productivity was observed for values above 0.6 G/B. A second objective was to assess varietal susceptibility in 62 cultivars. The susceptibility trait showed a wide range of variation from total resistance (7 cultivars: two C. sativa , one C. crenata and 4 Euro-Japanese hybrids) to high susceptibility (>0.6 G/B; 14 cultivars). Finally, size and proximate differences in galled and healthy leaves were studied to assess the changes due to infestation. Significant differences for leaf area, moisture, dry matter, ash, sugars, starch, and total carbohydrates were observed between the two types of leaves indicating a deep influence of the infestation on leaf functionality and on its photosynthetic capacity. KEYWORDS: Castanea , gall wasp, cynipid, resistance, leaf, chemical composition 1. INTRODUCTION Chestnut tree ( Castanea sativa Miller) is a multipurpose species with the role of fruit tree, wood resource and mountain landscape element in many areas of the Northern Hemisphere, where it is also interesting from a social point of view. However, in the last centuries, the sweet chestnut has been affected by major diseases, such as ink disease ( Phytophthora spp.) and canker blight (Chryphonectria parasitica (Murr.) Barr.), that have heavily changed its cultivation, production and economy. Among pests, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) is considered as the most invasive insect for chestnut; native of China, it was accidentally introduced in Japan (1941), Korea (1959) and North America (1974); more recently (spring 2002) its presence was firstly reported in Europe in the chestnut orchards and woods of Cuneo Province (Piemonte Region, Italy) (Brussino et al ., 2002). Japan, being the first Country to face the invasion of this alien species, was first in starting breeding programs (Pereira-Lorenzo et al ., 2010). Oho et al. (1970) cite a report of 1948 by Shirakami recounting that some cultivars belonging to C. crenata ('Akanaka', 'Shikatsume', 'Kishine' and 'Ginyose') were found without damage following the gall wasp infestation. In 1952 the Horticultural Research Station of Tsukuba began a chestnut-breeding program with the goal of developing cultivars resistant to the chestnut gall wasp. This program and some private breeding projects, released the cultivars ‘Tanzawa’, ‘Tsukuba’, and ‘Ishizuchi’ and other resistant varieties; in few years the chestnut production recovered. In spite of this initial success, the resistance was eventually overcome by ecotypes of the insect and cultivars became still susceptible to the chestnut gall wasp (Moriya et al., 2003). This problem induced researchers to evaluate a different strategy, based on biological control using the parasitoid Torymus sinensis Kamijo, with successful results. Yet, the development of resistant cultivars continued until the 1980s when varieties with increased resistance, such as ‘Kunimi’ and ‘Shiho’, were released (Saito, 2009). The studies on genotypes susceptibility were accompanied, over the years, by observations on the lifecycle of the insect, and by biochemical studies carried out to identify compounds responsible for the different cultivars reaction to the phytophagous (Oho and Shimura, 1970). In particular, Oho and Shimura (1970) considered the levels of tannins and the content of flavonols in bark. No significant differences in relation to the degree of susceptibility of the cultivars were found, among samples for tannins, flavonol content, instead, varied significantly. The damage of the infestation directly affect the leaves and shoots and, indirectly, the whole biomass. The leaf surface is reduced, yellowing is earlier and the amount of vegetative buds is, year by year, decreasing (Kato and Hijii, 1997). According to Dixon et al. (1986) the interruption of growth and fruiting, results in production losses up to 50-70% in the species C. mollissima , C. crenata and C. dentata . The infestation rarely causes plant death, but can favour it when other pathogens are present (Payne et al. , 1975). Despite these studies, still extremely important for the determination of damages caused by the chestnut gall wasp, the difference in composition between healthy tissues and infected tissues remains unknown. In fact, there are no studies at the biochemical level on chestnut galls, but only for oak and rose ones. In these plants, affected by several species of gall wasps (but not D. kuriphilus ), the gall, in addition to being a source of nutrients for the insect, also defends it from the attack of herbivores, increasing the concentration of phenols in the outer layers (Allison and Schultz, 2005). Regarding the characteristics of the tissues inside the gall, some authors claim "the nutritive hypothesis" according to which all the plant defence mechanisms are suppressed in the tissues of which the insect feeds (Price et al. , 1987; Bronner, 1992). The gall wasp is also adept at controlling the levels of nitrogen that keep the host within the usual limits for survival, even in cases in which the plant is fertilized (Hartley and Lawton, 1992). Cynipid gall formation is due to an extremely complex interaction between the insect and the host plant, in which the wasp communicates with the host to redirect normal plant development, providing shelter, nutrients and protection for the developing wasp larva in the form of a gall (Stone et al., 2002). Following the introduction of the cynipid in Italy in 2002, the Piedmont Region Administration promoted and founded a project aimed to find lasting solutions to control the pest. It was based on two strategies: the biological control of gall-wasp by the introduction from Japan of Torymus sinensis Kamijo (Hymenoptera: Torymidae) (Gibbs et al., 2011) and the study of plant response, both assessing production loss and determining cultivars susceptibility to the insect. In this paper the results of the work carried out from 2004 to 2013 to study plant response to gall wasp are presented. Data on production losses were recorded (2006-2012) in a chestnut orchard located in a highly infested area and were used to classify chestnut response in terms of yield. Furthermore, gall wasp infestation susceptibility was studied on both local and international cultivars under controlled conditions (2004-2013). In 2012 we used chemical analyses to determine the amount of the basic constituents present in healthy leaves compared with leaves with galls of the same plant, to evaluate the decrease of resources available to the plant for the production of the fruit and for the vegetative growth.